The present invention concerns an optical element that comprises a base body and an optically effective layer system of which at least one layer system surface contacts the base body according to features of the invention.
The invention also comprises a related manufacturing process the utilization of such a component or process as well as an optical projection arrangement with such a component.
In DE-40 33 842 a cuboid optical element composed of dichroitic layers is referred to as a xe2x80x9cdichroitic prism.xe2x80x9d
In this application the term X-cube is used.
The present invention starts with the problems that exist with known X-cubes, for example, as described in DE-40 33 842, or that occur in its manufacture. The present invention which was developed in order to find a solution to the problems with such elements, can be applied to a number of other optical elements.
For this reason this description begins with the specific problems to be solved on X-cubes and based thereon explains the application of the invention in more general terms.
Based on FIG. 1 the functional principle of an X-cube is explained. Optical elements of this type are principally used in projectors in order to recombine the red/green and blue channels in the spectral range of the visible light. As shown in FIG. 1 such an X-cube 1 comprises-four individual prisms 2a to 2d which can, for example, be made of BK7 glass. In their cross-section they form right-angled isoceles triangles with an angle of 90xc2x0, usually with a tolerance of over xc2x160 angular seconds and hypotenuse angles of 45xc2x0 with tolerances of a few angular minutes. The length of the hypotenuse is typically between 5 mm and 50 mm, preferably 40 mm. Embedded between the two prism pairs 2a and 2b on the one side, 2d and 2c on the other side, there is an optically effective system 5 that largely reflects visible light in the blue range but largely transmits visible light in the green or red range. FIG. 1 shows a part of the blue reflector layer system as a color splitting system, labeled 5xe2x80x2, the other 5xe2x80x3.
Embedded between the two prism pairs 2a and 2d on the one side, 2b and 2c on the other side there is an additional, optically effective layer system 7, that largely reflects light in the red range but largely transmits light in the green range and the blue range. In FIG. 1 also the two legs of the red reflector layer system are shown as a color splitter system, labeled 7xe2x80x2 and 7xe2x80x3.
On the X-cube there are three input channels for red, green and blue light from corresponding sources, for example, LCD controlled, and an output channel with the recombined input signals. On the reflector systems, between each of said prism pairs, the correspondingly colored light, and particularly S-polarized light with an incidence of less than 45xc2x0 is reflected. In addition the hypotenuse surfaces of the prisms 2 can be and usually are coated with an antireflection layer system.
Because the pixels of the red-blue-green input channels should converge as accurately as possible, the angle tolerances on the prism 2 and in the assembled X-cube must be very narrow.
Large tolerances result in a poor imaging quality, because the pictures do not accurately converge: blurring or color fringes occur.
Location 9, shown with dashes in FIG. 1 where the four individual prisms 2 meet, is also located within the imaging optical path. Optical interferences created in this location manifest themselves, as mentioned for example, as a blurred picture in the output channel OUT. It is a requirement of such elements and their manufacturing process to minimize the interferences, particularly in this location 9.
From DE-40 33 842, for example, it is known that X-cubes can be manufactured from four prisms 2 according to FIG. 1. The four individual prisms are first manufactured in their exact dimensions through milling, grinding and polishing. Subsequently they are coated with the appropriate layer system along their legs, and possible on their hypotenuse surfaces with an antireflection coating. Finally the coated individual prisms 2 are cemented together.
Disadvantages of the Known Processes and Known X-cubes
The handling effort required for manufacturing the X-cubes as described, for example, in DE-40 33 842, is very high: First, each of the three lateral sides of each individual prism 2 must be mounted or fixed by plastering, blocking or wringing as shown in FIG. 1 before the glass can be worked. Subsequently the surfaces must be cleaned for coating the individual prisms 2, and then mounted and dismounted for the coating process. On an average two sides per individual prism need to be coated. This laborious handling considerably raises the production costs for such X-cubes.
From FIG. 1, particularly location 9, it is evident that the coating of the red and blue reflecting layer systems must be executed in such a way that the coating does not wrap around the 90xc2x0 edges of the individual prisms. This requires sophisticated coating fixtures or masking of the legs on which no coating may be deposited. In this respect we refer to U.S. Pat. No. 2,737,076 (Rock et al.).
During the coating and the entire handling of the individual prisms 2, the 90xc2x0 prism edges are exposed without protection, that is, especially those edges which according to the foregoing explanation must be very accurate. This inevitably leads to chipping unless laborious precautions to protect these edges are taken, which again increases the costs.
If, for example, anything goes wrong during the coating of the individual prisms 2, such an individual piece must be remounted, ground, and repolished, otherwise it would have to be discarded. Correction processes are at best very difficult to implement.
Cementing in the exact relative position of the individual prisms 2 is very difficult and laborious. Complicated processes such as described in DE-40 33 842 are required. Prisms are cemented individually which is time-consuming and therefore costly.
Independently of said disadvantages the known process results in a structure in location 9 shown in FIG. 1, as can be seen from the detail in FIG. 2. The same reference marks as in FIG. 1 are used. Item number 11 identifies cemented joints.
From this it is evident that the cemented joints 11 cause an interruption of the red light reflection layer system 7 (consisting of 7xe2x80x2 and 7xe2x80x3) as well as the blue light reflection layer system 5 (consisting of 5xe2x80x2, and 5xe2x80x3).
As the X-cube is manufactured by cementing the individual prisms 2 whose 90xc2x0 edges have been exposed to external influences without protection, faults occur almost inevitably in location 9 due to chipping defects along the 90xc2x0 edges of the individual prisms.
The purpose of the present invention is to propose an optical element, in particular an X-cube, which is not afflicted by the disadvantages explained on the basis of FIG. 2.
It is also the objective of the present invention to propose a manufacturing process that is not afflicted by said disadvantages in production, in particular of said X-cubes. The manufacturing process to be found should by highly economical, afford greater accuracy, and require fewer process steps.
In an optical element of the type referred to at the beginning, this is achieved by depositing on the body a second layer system that adjoins the surface of the first layer system at an angle. In this way the first mentioned, optically effective layer system is areally continuous and the second layer system adjoins one of the surfaces of the first one without gap. A structure as has been explained based on FIG. 2 is avoided: According to the invention, with reference to FIG. 2, one of the layer systems, preferably 7, is continuous; individual sections 7xe2x80x2, 7xe2x80x3 no longer exist. According to the invention a second layer system, preferably system 5, 5xe2x80x2 adjoins that continuous layer system 7, and in the case of an X-cube also a third layer system, 5xe2x80x3. This is not illustrated in FIG. 2 which shows the familiar intersection structures.
Characteristic for the process according to the invention is that for solving the aforementioned task one surface each is created on at least two sub-bodies of the base body of the element, where said two surfaces are complementary to each other on at least two sub-bodies, that is, they fit together with close tolerances. Subsequently at least one of these complementary surfaces is coated with an optically effective layer system, in particular the red or blue reflection layer system, if the element to be produced is an X-cube.
Subsequently, said sub-bodies are joined, for example, by cementing along said complementary surfaces with their now embedded layer system. A composite sub-body is thus formed. On the composite sub-body one surface that is common to at least two sub-bodies is processed which is at an angle to the complementary, interconnected surfaces, so that the complementary surfaces along which the sub-bodies are connected intersect the common surface to be processed. Finally another optically effective layer system is deposited along this jointly processed surface.
The preferred design versions of the element or process according to the invention are specified in the dependent claims. The element according to the invention is preferably used as an X-cube, or the process according to the invention is preferably used for manufacturing such X-cubes.
An optical projection arrangement with at least one element designed as an X-cube according to this invention has significantly reduced optical interference, especially in the center area 9 shown in FIG. 2, and due to the proposed production process it can be manufactured more economically and more accurately.